Flighting for dehydrator drum and method

ABSTRACT

A method and apparatus for drying a material utilizes a rotatable, elongated drum adapted to be coupled with a furnace and means for achieving pneumatic conveying of a material to be dried. The pneumatic conveying medium is controlled so that at least a portion of the material gravitates from the conveying stream until a portion of the water has been removed. The gravitational portion of the material is picked up at the outer surface of the drum by a plurality of vanes which rotate with the drum. Each vane includes one or more cleats which cause the material to effectively &#39;&#39;&#39;&#39;dribble&#39;&#39;&#39;&#39; from the vanes rather than dropping in clumps as the material reaches a point above the center of the drum. As the material moves from the side of the drum toward the center of the drum it is caught by interference structures disposed axially of the drum in radially spaced relationship with a plurality of the structures being placed longitudinally along the drum. Each structure presents a planar surface portion having opposed side edges. At least one side edge extends at an acute angle relative to a perpendicular bisector of the longitudinal axis of the drum and a sidewall extends upwardly from one side edge to effectively push material gravitating onto the planar surface in a predetermined direction independent of the direction of movement of the conveying medium. This forces the material toward either the inlet or the outlet of the drum and can increase or decrease the retention time of the material in the drum by several fold.

United States Patent n91 Thompson 1 FLIGHTING FOR DEHYDRATOR DRUM AND METHOD [76] inventor: Stanley P. Thompson, PO Box 8073.

Topeka, Kans. 66608 22 Filed: Feb. 28. 1973 211 Appl. No.: 336,445

[52] US. Cl. ..'I'34/108, 34/136, 34/126, 432/103 [51] Int. Cl. F26g 11/02 [58] Field of Search 34/10, 108. 109. 124-128, 341134-138. 5. 168', 432/14, 103, 104, 107-109. 118. 151

3.407.511 10/1963 Camm.... 34/109 3,717,937 2/1973 Thompson 14/108 263.584 8/1882 Rice 34/137 3,720,253 3/1973 Ballas ct al. 34/22 Primary Examiner-John .l. Camby Assistant Examiner-Henry C. Yuen Attorney, Agent. or Firm-Lowe. Kokjer, Kirchcr, Wharton & Bowman 1 1 ABSTRACT A method and apparatus for drying a material utilizes 1 Mar. 26, 1974 a rotatable, elongated drum adapted to be coupled with a furnace and means for achieving pneumatic conveying of a material to be dried. The pneumatic conveying medium is controlled so that at least a portion of the material gravitates from the conveying stream until a portion of the water has been removed. The gravitational portion of the material is picked up at the outer surface of the drum by a plurality of vanes which rotate with the drum. Each vane includes one or more cleats which cause the material to effectively "dribble" from the vanes rather than dropping in clumps as the material reaches a point above the center of the drum. As the material moves from the side of the drum toward the center of the drum it is caught by interference structures disposed axially of the drum in radially spaced relationship with a plurality of the structures being placed longitudinally along the drum. Each structure presents a planar surface portion h2l\'- ing opposed side edges. At least one side edge extends at an acute angle relative to a perpendicular bisector of the longitudinal axis of the drum and a sidewall extends upwardly from one side edge to effectively push material gravitating onto the planar surface in a predetermined direction independent of the direction of movement of the conveying medium. This forces the material toward either the inlet or the outlet of the drum and can increase or decrease the retention time of the material in the drum by several fold.

15 Claims, 9 Drawing Figures FLIGHTlNG FOR DEHYDRATOR DRUM AND METHOD This invention relates to drying apparatus and, more particularly. to improved flighting for a drying drum and a method of drying a material in a drum.

An important consideration in the drying of any material is proper distribution of the material to be dried within the drying zone. Distribution is a particular problem in the drying of crops such as alfalfa because ol'the tendency for the crop to bunch together. This results in inadequate drying of some of the alfalfa and overdrying and even charring of some of the alfalfa.

Any naturally occurring material will have some portions high in moisture content and other portions low in moisture content. The fact that the dryer must be designed to dry the material of relatively high moisture content has heretofore resulted in some charring and burning of material of low moisture content. This is a substantial factor in atmospheric pollution attributable to crop dryers. Ideally, that portion of the material having a higher moisture content would be retained in the dryer for a relatively long period of time while material of a lower moisture content would pass on through the dryer. A dryer meeting these design criteria has not been commercially available prior to the introduction of the present invention.

It is an object of the present invention to provide apparatus for drying a material where the moisture content of the material varies over a wide range and that portion of the material having a relatively high moisture content is retained within the dryer for a substantial period of time after the portion of the material having a much lower moisture content has passed through the dryer.

Another object of this invention is to provide a method and apparatus for drying a material which is of a density such that the material cannot be satisfactorily conveyed by pneumatic means alone wherein the material is forced through the dryer by mechanical conveying means.

Another object of the invention is to provide internal flighting for a dehydrator drum whereby the utilization of folds in the flighting material results in substantially increased strength thereby allowing a lighterweight material to be utilized for construction of the flighting.

As a corollary to the above objects, an important aim of the invention is to provide a method and apparatus for drying a material as described in the foregoing objeets wherein the material is prevented from "bunching" in the dryer thereby facilitating faster and more uniform drying.

in the drawings:

FIG. I is a side elevational view ofa dehydrator drum and associated structure as could be utilized in the present invention;

FIG. 2 is an enlarged vertical cross-sectional view taken through the dehydrator drum of FIG. I and illustrating the means of support for the internal flighting, which has been deleted from the drawing for clarity;

FIG. 3 is a vertical, cross-sectional view taken through the drum taken along a line extending at an angle of 90 from the sectional line of FIG. 2, and on a reduced scale from FIG. 2 with the internal flighting again being deleted for clarity;

FIG. 4 is a greatly enlarged cross-sectional view through the longitudinally extending shaft which supports the internal flighting and illustrating the hangar arrangement for supporting this shaft;

FIG. 5 is a fragmentary. side elevational view of the shaft shown in FIG. 4 viewing the shaft from a position 90 removed from the sectional line of FIG. 4;

FIG. 6 is an enlarged, horizontal, cross-sectional view through the dehydrator drum illustrating the internal flighting arrangement within the drum;

FIG. 7 is an enlarged perspective view of the interference structure which forms a part of the internal flighting for the drum along with its associated supporting elements;

FIG. 8 is a side elevational view of an alternative form for the interference structure shown in FIG. 7; and

FIG. 9 is a side elevational view of still another alternative form of the interference structure.

Referring initially to FIG. I of the drawings, a typical dehydrator includes a drying drum I0 in the form of an elongated cylindrical body 12 which is mounted for rotation upon bearings 14. Body 12 has an inlet end to and an outlet end I8 through which the material to be dried passes. The cylindrical sidewall 20 of body I2 delines a drying zone to which hot air is supplied by a furnace 22. Furnace 22 is coupled with drum I0 through a connecting section 24. Furnace 22 is designed to burn a combustible fuel and hot gases of combustion are forced into the drying zone by a blower fan 26. A material inlet conveyor 28 communicates with the inlet end of body I2 to introduce material to be dried into the in terior of drum 10.

A second blower fan 30 has its intake in communication with the interior of body 12 through a conduit 32. Thus, fan 30 cooperates with fan 26 to provide a pneumatic conveying medium to move material to be dried through drum [0. The outlet from blower 30 communicates with a conduit 34 which may be utilized to direct the dried material to a separator (not shown) to remove the dehydrated material from the airstream and forward it for subsequent processing operations. Dampers 36a and 36b disposed in conduits 32 and 34 respectively are operated by common control circuitry 38 which also controls a valve 40 in a fuel line 42 which directs combustible fuel to furnace 22.

In the drying of a forage crop such as alfalfa or other naturally occurring materials where there is substantial variation in the relative moisture content of different portions of the material, it is particularly important that as much surface area of the material particles as possible be exposed to the drying influence of the hot gases passing through body 12. It is desirable to hold the material of a relatively high moisture content in the drying zone for a longer period of time than the relatively dry material. It is also desirable to hold the portion of the material of relatively high moisture content in the high temperature area of the drying zone where it can ahsorb more energy faster. This high temperature area is located near the center of the zone rather than at the outer periphery adjacent the sidewall of elongated body 12. To these ends, the interior of body 12 is provided throughout its length with flighting adapted to catch the portion of the material gravitating to the outer periphery of the drying zone upon rotation of body [2 and to hold this material until it reaches a point above the center of the drying zone where it is gradually dropped back toward the center. As the material gravitates toward the center of the drying zone.

it is again caught and held for a period of time in this high temperature area of the zone while the drum continues to rotate. Subsequently, the material is forced in a predetermined direction which, in the case of a crop such as alfalfa, will be backwards in the general direction of the material inlet to drum 12. This substantially increases the retention time of that portion ofthe material having a relatively high moisture content while the drier portion of the material will be pneumatically conveyed on through and out of the drying zone.

The flighting to accomplish the foregoing objectives for handling the material in drum will now be described in detail. A shaft 44 extending longitudinally of body 12 from inlet end 16 to outlet end 18 is rigidly coupled with sidewall 20 by a plurality of hangars 46. As best illustrated in FIGS. 4 and 5, each hangar 46 comprises an arcuate stretch 48 which at least partially surrounds shaft 44 and merges into opposed elongated linear stretches S0 and 52. Stretches 50 and 52 diverge outwardly from shaft 44 and terminate in opposed ends which are secured to sidewall 20 in circumfcrentially spaced relationship at the outer periphery of the drying zone defined by body 12. A plurality of the hangars 46 are normally disposed in spaced relationship along the length of body 12.

Rigidly secured to shaft 44 are a plurality of radially extending, circumferentially spaced support elements designated generally by the numeral 54 which mount interference structure designated generally by the numeral 56. It is to be understood that a plurality of support structures 54 and interference structures 56 are disposed longitudinally of shaft 44 throughout the entire lenght ofbody 12. Elements 54 are braced by cross ties 58 which are rigidly secured to the elements and span the distance between adjacent elements. A plurality of the ties 58 are disposed in spaced relationship along the length of body 12.

Since each support element 54 and interference structure 56 coupled therewith is identical only one of each of these components will be described in detail. Each support element 54 is constructed from sheet metal or other suitable material and comprilel a planar surface portion 58 with opposed converging sidewalls 60 and 62 which are integral with portion 58. The uppermost end of element 54 is cut at an acute angle to present an inclined seat for structure 56. The interference structure is welded or otherwise secured to element 54 and it will be appreciated that the sidewalls 60 and 62 present gusset plates at their uppermost ends which strengthen and support structure 56.

Each interference structure 56 is thus disposed at an acute angle relative to the horizontal at the end of element 54 (when the latter is in a vertical position). Each structure 56 comprises a generally flat planar surface 64 having opposed converging side edges 66 and 68. At least one edge (66 in the drawing) extends at an acute angle to a hypothetical perpendicular bisector of the longitudinal axis of the drum. Extending upwardly from surface 64 at side edges 66 and 68 are opposed sidewalls 70 and 72 respectively. Also extending upwardly from surface 64 are opposed end walls 74 and 76 which extend between sidewall: 70 and 72.

It is to be understood that element 54 and interference structure 56 are normally disposed IO that side edge 68 is perpendicular to the longitudinal axis of shaft 44. Thus, side edge 66 converges toward side edge 68 at an acute angle which may be varied according to the drying requirements for a particular material. It is to be noted that sidewall 70 extends upwardly above surface 64 a substantial distance at its highest point and it is desirable that this distance be at least three inches although a lesser or greater height may be utilized in conjunction with the requirements of a speciftc material being dried. As illustrated in FIG. 7. a plurality of elements 54 and structures 56 are disposed in sidc-by-side relationship along the length of body l2.

Manifestly, interference structures 56 travel in a first circular path during rotation of drum to and spaced radially outward from structures 56 and secured to sidewall 20 in eircumferentially spaced relationship are a plurality of vanes designated generally by the numerals 78 and 80. Although the construction of the vanes spaced around sidewall 20 may be varied to some de gree, each of the vanes is characterized by a general shape as represented by one or the other of vanes 78 and 80. Referring first of all to the vane designated by the numeral 78 in FIG. 6, each such vane comprises a substantially flat panel 82 of generally planar construction having one end secured by welding or the like to the inner surface of wall 20. To this end, a gusset support 84 extending between sidewall 20 and the bottom of panel 82 further supports vane 78. Each panel 82 has a width ofapproximately six to ten inches and a wall 86 extends upwardly at either side edge of the panel. The sidewalls 86 have been deleted from all but one of vanes 78 shown in PK]. 6 to reveal the interior eonstruction of the vane. It will be seen from viewing FIG. 6 that each panel 82 extends radially inwardly of sidewall 20 and terminates in a lip 88 which corresponds to end wall 74 for structure 56. Spaced intermediate lip 88 and the end of panel 82 which is secured to sidewall 20 is an upwardly projecting cleat 90.

The construction of vane is identical to the construction of vane 78 except for the fact that panel 82 is turned upwardly at an acute angle prior to terminating in lip 88. Vane 80 is also provided with opposed walls 86 and an upwardly projecting cleat )0. Walls 86 have also been eliminated from all but one of vanes 80 shown in FIG. 6 to reveal the interior construction of the vanes. It is anticipated that there will be some variation in the degree of bend of each of vanes 80 circumferentially spaced around drum 10. It is to be understood that a plurality of vanes 78 and 80 are disposed in side-by-side relationship longitudinally of body 12. While it is preferable to construct vanes 78 and 80 as described above with walls 86 for added strength utilizing a lighterweight material, the peripheral vanes may also be constructed in a continuous longitudinally extending manner without walls 86 as described in my earlier U.S. Pat. No. 3,717,937.

In operation. fuel is burned in furnace 22 and the hot combustion gases are directed into the drum by blower 26. Material to be dried, such as alfalfa, is conveyed to the interior of the drum by conveyor 28, and the drum is rotated about its longitudinal axis through appropriate drive means, not shown. Blower fan 30 is also operated to assure a sufficient flow of combustion gases and air longitudinally of the drum to provide a pneumatic conveying medium to move material from the inlet end 16 to outlet end 18.

The lifting force factor of the pneumatic conveying medium is regulated through use of dampers 36a and 36b so that the medium is incapable of supporting that portion of the material to be dried which is relatively high in moisture content. Thus, this portion of the material will immediately gravitate to the outer periphery of the drying zone where it is caught by vanes 78 and 80 and held by the latter as drum it) rotates. The vanes will move the material upwardly to a location above the center of the drying zone at a point circutnferentially spaced from the point where the material was initially caught and then as the vanes are moved to an over center position the material will gravitate toward the center of the drying zone. The different shapes of the vanes insure that the material release point for the various vanes is reached at different positions of rotation of the drum. Thus, a substantially uniform curtain of material is released by successive vanes for gravitation through the pneumatic conveying medium toward the center of the drying zone. Cleats 90 disposed on the vanes assure a breakup of any bunches of material as the latter slides along panel 82. Further breakup of any bunches occurs as the material strikes lip 88 before leaving the vanes.

Any material which is relatively low in moisture content and thus is dried relatively quickly will be picked up by the pneumatic conveying medium and moved quickly along the length of body 12. Until the material has travelled a substantial distance along the length of body 12, however, the major portion of the material will be too heavy to be supported by the conveying medium.

Accordingly, as the heavier and higher moisture content material gravitates from vanes 78 and 80 it will move downwardly toward the center of the drying zone until it is caught by interference structures 56. By positioning structures 56 at an angle of between and relative to a horizontal plane (when elements 54 extend perpendicular to the plane) the structures are in a position to catch material gravitating from vanes 78 and 80 much sooner than would be the case if they were disposed in a horizontal position. Structures 56 hold the material relatively close to the center of the drying zone for maximum absorption of heat. Manifcstly, the fact that sidewall extends substantially above the plane of planar surface 64 helps prevent any material from being blown off the surface by the conveying medium. On the other hand, the lifting force of the conveying medium can be maintained at a relatively high level to assure removal ofdried particles from the drum since interference structures 56 are designed to effectively hold the heavier high moisture content particles against the action of the conveying medium.

For a crop such as alfalfa the problem heretofore encountered with drying drums is that the relatively high moisture content material cannot be held within the drum for a sufficient period of time to assure drying without the danger ofeharring and burning that portion of the material which is relatively low in moisture content. With a drum constructed according to the teachings of the present invention, structure 56 is constructed with the side edge of planar surface 64, which is distal inlet end 16 of body 12, extending at an acute angle relative to a perpendicular bisector of the longitudinal axis ofdrum 12. With sidewall 70 extending upwardly adjacent this edge of surface 64, and with body 12 rotating in a clockwise direction when viewing HO. 6, material gravitating onto surface 64 will be forced backward toward inlet end l6 as it slides along surface 64. The material will be moved back toward the inlet a distance equal to the difference between the length of end wall 74 and end wall 76.

End walls 74 and 76 also facilitate retention of the material on surface 64 and end wall 74 serves in the same manner as lips 88 of vanes 78 and 80 to break up any bunches ofmaterial which were not previously broken. The material held by structures 56 will ultimately be released to again gravitate toward the outer periph ery of the drying zone at a location spaced circumferentially from the point where the material was initially caught. Although most of the material will be caught by interference structures 56 any material gravitating onto elements 54 will be held by these elements as a result of their construction in an analogous manner to interference structures 54.

As shown in FIG. 8, in some instances it may be desirable to incorporate a cleat 190 on the surface 64. Cleat 190 projects above the surface and extends between sidewalls 70 and 72 to further facilitate break up of material in the same manner as cleats on vanes 78 and 80.

In FIG. 9. another alternative form of the invention is illustrated. Here a second interference structure 156 is secured to element 54 spaced radially inward from first structure 56. lnterference structure 156 is identical to structure 56 except for the fact that sidewall projects above planar surface I64 only to the same extent as sidewall l72. Corresponding reference numerals plus I00 have been used to identify components of structure 156 analogous to corresponding components of structure 56.

The drying drum of the present invention may also be utilized with relatively high density crops such as grains which, in many instances, are incapable of being conveyed solely by pneumatic means. This permits utilizing a drying drum with a pneumatic conveying medium, which is by far the most effective means of drying such a relatively dense material. By reversing the flow of material through body 12, i.e., utilizing outlet end 18 as the inlet for material to be dried as well as the inlet for drying gases and the conveying medium, a material such as corn can be dried in drum to. The reversal of flow through body 12 has the effect of changing the direction of rotation of the body to counterclockwise and locating the angularly disposed sidewall 66 at the side of surface 64 which is nearest the material inlet end. Thus, as the material is picked up by vanes 78 and 80 and is allowed to gravitate onto surface 64, sidewall 70 which is now nearest the material inlet and will force the material in the general direction of the material outlet. A substantial "angering" effect results which facilitates movement of the material in cooperation with the conveying medium. Manifestly, although not essential for use of drum 10 in the manner just described, it may also be desirable for side edge 68 of surface 64 to extend at an acute angle relative to a perpendicular besector of the longitudinal axis of the drum. Sidewall 72 would likewise extend along the angularly disposed side edge to enhance the angering effect.

While it is preferable from the standpoing of ease and economy of construction to construct structures 56 with one side edge 68 substantially parallel to a perpendicular bisector of the longitudinal axis of the drum while the other side edge converges toward the first edge, it will be appreciated that in some instances it may be desirable to have the two side edges and the corresponding sidewalls extending in parallel relationship at an acute angle relative to the hypothetical perpendicular bisector of the longitudinal drum axis.

Having thus described the invention, I claim:

1. A drying drum adapted to be coupled with means for providing a pneumatic conveying stream to facilitate movement of material to be dried through the drum, and means for rotating the drum about its longitudinal axis; said drying drum comprising:

an elongated hollow body having a material inlet and an outlet;

a plurality of vanes eoupled with the body and spaced circumferentially around and longitudinally of the inner surface of the body,

a plurality of eircumferentially spaced interference structures coupled with said drum at a location spaced radially inwardly from said vanes,

a plurality of said structures being disposed longitudinally of the drum,

each of said structures presenting a generally planar surface having opposed side edges, at least one of said edges extending at an acute angle to a perpendicular bisector of the longitudinal axis of the body,

each of said structures further being provided ith a first sidewall extending upwardly adjacent one of the side edges,

whereby as the body is rotated and a material is moved from the inlet to the outlet under the influence of the pneumatic conveying medium, material gravitating onto said vanes is moved to a location from which it gravitates onto said structures and is forced in a predetermined direction independent of the direction of movement of the conveying medium by said structures as the latter rotate with the drum.

2. The invention of claim I. wherein is included a radially extending support element coupled with the drum and rigid with each of said structures.

3. The invention of claim 2, wherein each of said elements comprises a planar surface portion and a first sidewall extending outwardly from said portion at a location corresponding to the location of the sidewall on the structure.

4. The invention of claim 3, wherein each of said elements comprises a second sidewall extending outwardly from the planar portion, each of the sidewalls of said elements having an end disposed in abutting relationship to the structure whereby to present gusset supports for the structure.

5. The invention of claim 4, wherein said sidewalls of said elements converge as they approach said structure.

6. The invention of claim 2, wherein a second interference structure is rigidly coupled with said support element spaced radially inwardly from each of the firstmentioned structures.

7. The invention of claim 2, wherein is included a shaft extending longitudinally of said body and rigidly coupled with the latter, each of said elements being rigidly secured to the shaft.

8. The invention of claim 7, wherein is included a plurality of elongated supports coupling said shaft with said body, each support having a first end secured to the inner surface of the body, an arcuate stretch at least partially encircling the shaft, and a second end secured to the inner surface of the body at a point spaced from the first end.

9. The invention of claim I, wherein each of said structures is provided with a second sidewall extending upwardly from the other side edge.

10. The invention ofclaim 1, wherein each of said structures is provided with a first end wall extending upwardly from said surface to facilitate retention of material on the surface.

I]. The invention of claim 10, wherein each of said structures is provided with a second end wall extending upwardly from said surface to further facilitate retention of material on the surface.

12. The invention of claim 1, wherein said one side edge is disposed on the side of said surface distal from said inlet, and said first sidewall extends upwardly from said surface at said one side edge whereby as the drum is rotated in a clockwise direction material moving from the inlet to the outlet is forced back toward said inlet.

13. The invention of claim 12, wherein said first sidewall projects upwardly to a distance of at least three inches above the plane of said surface.

14. The invention of claim 1, wherein said one side edge is disposed on the side of said surface nearest said inlet, and said first sidewall extends upwardly from said surface at said one side edge whereby as the drum is rotated in a counterclockwise direction material moving from the inlet to the outlet is forced toward said outlet.

wardly from said surface between said side edges.

O i U i t 

1. A drying drum adapted to be coupled with means for providing a pneumatic conveying stream to facilitate movement of material to be dried through the drum, and means for rotating the drum about its longitudinal axis; said drying drum comprising: an elongated hollow body having a material inlet and an outlet; a plurality of vanes coupled with the body and spaced circumferentially around and longitudinally of the inner surface of the body; a plurality of circumferentially spaced interference structures coupled with said drum at a location spaced radially inwardly from said vanes, a plurality of said structures being disposed longitudinally of tHe drum, each of said structures presenting a generally planar surface having opposed side edges, at least one of said edges extending at an acute angle to a perpendicular bisector of the longitudinal axis of the body, each of said structures further being provided with a first sidewall extending upwardly adjacent one of the side edges, whereby as the body is rotated and a material is moved from the inlet to the outlet under the influence of the pneumatic conveying medium, material gravitating onto said vanes is moved to a location from which it gravitates onto said structures and is forced in a predetermined direction independent of the direction of movement of the conveying medium by said structures as the latter rotate with the drum.
 2. The invention of claim 1, wherein is included a radially extending support element coupled with the drum and rigid with each of said structures.
 3. The invention of claim 2, wherein each of said elements comprises a planar surface portion and a first sidewall extending outwardly from said portion at a location corresponding to the location of the sidewall on the structure.
 4. The invention of claim 3, wherein each of said elements comprises a second sidewall extending outwardly from the planar portion, each of the sidewalls of said elements having an end disposed in abutting relationship to the structure whereby to present gusset supports for the structure.
 5. The invention of claim 4, wherein said sidewalls of said elements converge as they approach said structure.
 6. The invention of claim 2, wherein a second interference structure is rigidly coupled with said support element spaced radially inwardly from each of the first-mentioned structures.
 7. The invention of claim 2, wherein is included a shaft extending longitudinally of said body and rigidly coupled with the latter, each of said elements being rigidly secured to the shaft.
 8. The invention of claim 7, wherein is included a plurality of elongated supports coupling said shaft with said body, each support having a first end secured to the inner surface of the body, an arcuate stretch at least partially encircling the shaft, and a second end secured to the inner surface of the body at a point spaced from the first end.
 9. The invention of claim 1, wherein each of said structures is provided with a second sidewall extending upwardly from the other side edge.
 10. The invention of claim 1, wherein each of said structures is provided with a first end wall extending upwardly from said surface to facilitate retention of material on the surface.
 11. The invention of claim 10, wherein each of said structures is provided with a second end wall extending upwardly from said surface to further facilitate retention of material on the surface.
 12. The invention of claim 1, wherein said one side edge is disposed on the side of said surface distal from said inlet, and said first sidewall extends upwardly from said surface at said one side edge whereby as the drum is rotated in a clockwise direction material moving from the inlet to the outlet is forced back toward said inlet.
 13. The invention of claim 12, wherein said first sidewall projects upwardly to a distance of at least three inches above the plane of said surface.
 14. The invention of claim 1, wherein said one side edge is disposed on the side of said surface nearest said inlet, and said first sidewall extends upwardly from said surface at said one side edge whereby as the drum is rotated in a counterclockwise direction material moving from the inlet to the outlet is forced toward said outlet.
 15. The invention of claim 1, wherein is provided cleat means rigid with said surface and projecting upwardly from said surface between said side edges. 